不同含铬废水对薏苡人工湿地残根分解及铬化学形态的影响

Effects of different chromium containing wastewater on residue decomposition and chromium chemical forms in Coix lacryma-jobi constructed wetland

关键词:  铬, 人工湿地, 铬化学形态, 残根分解, 水质

Key words:  chromium, constructed wetland, chemical form of chromium, residue decomposition, water quality

摘要:

为探讨生活污水与营养液两种不同的水源对六价铬[Cr(Ⅵ)]污染人工湿地残根分解及铬化学形态转化的影响,该研究通过构建微型薏苡人工湿地处理含铬废水 [分别以生活污水(DWS)和1/2 Hoagland营养液(HNS)配制含0、20、40 mg· L^-1 Cr(Ⅵ)的配制液作为模拟含铬废水],采用埋根分解法,研究残根的分解动态,以及铬化学形态转化规律。结果表明:(1)20、40 mg· L^-1 Cr(Ⅵ)胁迫下,薏苡的生长均受到抑制,HNS处理株高和茎径均大于DWS处理,但HNS处理的株高和茎径受Cr(Ⅵ)抑制程度大于DWS处理。(2)薏苡残根分解速率随Cr(Ⅵ)处理浓度的提高而降低,HNS处理残根分解速率大于DWS处理。分解60 d后,DWS处理条件下,20、40 mg· L^-1 Cr(Ⅵ)处理残根铬含量比埋根初期分别降低了11.70%、8.09%,HNS处理下分别下降了15.80%、18.42%。20、40 mg· L^-1 Cr(Ⅵ)处理薏苡残根的残渣态铬占比均随埋根时间的延长而降低,而乙醇提取态铬和去离子水提取态铬占比增大,醋酸结合态铬占比则显著增大。(3)残根分解初期,HNS和DWS处理出水中的COD、TN、NH₄-N以及总铬含量均有提高,而后降低,变化趋势与残根分解进程一致,HNS处理人工湿地对废水中铬的去除效率更高。该研究结果表明在人工湿地植物收割后,根系分解可短时间内提高出水中铬含量,适当改善污水中营养状况,可以促进残根分解和湿地对铬的去除。

Abstract:

To investigate the effects of two different water sources, domestic sewage and nutrient solution, on residue decomposition and the transformation of chromium chemical forms in Cr(Ⅵ)contaminated constructed wetlands, a micro Coix lacryma-jobi constructed wetland was constructed to treat chromium containing wastewater [using domestic sewage(DWS)and 1/2 Hoagland nutrient solution(HNS)as simulated solutions containing 0, 20, 40 mg· L^-1 Cr(Ⅵ), respectively]. By using the buried root decomposition method, the decomposition dynamics of residual roots and the transformation pattern of chromium chemical forms were studied. The results were as follows:(1)Under 20 and 40 mg· L^-1 Cr(Ⅵ)stress, the growth of C. lacryma-jobi was inhibited. The plant height and stem diameter of HNS treatment were greater than those of DWS treatment, but the plant height and stem diameter of HNS treatment were more inhibited by Cr(Ⅵ)than those of DWS treatment.(2)The decomposition rate of C. lacryma-jobi residual roots decreased with the increase of Cr(Ⅵ)concentration, and the decomposition rate of HNS treatment was higher than that of DWS treatment. After 60 d of decomposition, under DWS treatment, the residual root chromium content of 20 and 40 mg· L^-1 Cr(Ⅵ)treatment decreased by 11.70% and 8.09% respectively compared with that at the initial stage of root burial, while under HNS treatment, the residual root chromium content decreased by 15.80% and 18.42% respectively. The percentage of residual chromium in C. lacryma-jobi root residues at 20 and 40 mg· L^-1 treatments decreased with the extension of root burial time, while the percentage of ethanol-extracted chromium and deionized water extracted chromium increased, and the percentage of acetic acid bound chromium increased significantly.(3)In the early stage of residue decomposition, the COD, TN, NH₄-N, and total chromium content in the effluents treated with HNS and DWS increased, and then decreased. The trend of change was consistent with the residue decomposition process. HNS treated constructed wetlands were more efficient in removing chromium from wastewater. The research results indicate that after harvesting plants in constructed wetlands, root decomposition can quickly increase the chromium content in the effluent, and appropriately improve the nutritional status in wastewater, which can promote residue decomposition and removal of chromium by wetlands.